In electronics, a trans-impedance amplifier (TR) is essentially a current-to-voltage converter. The TIA may be configured to amplify an input current from an electrical component, such as a sensor or photodiode, to a usable voltage in a particular circuit. TIAs are typically implemented using operational amplifiers.
FIG. 1 illustrates a prior art TIA 100, having a core TIA 110, a linear variable gain amplifier (VGA) 120 and an output stage 130. For such a typical, high linear TIA 100, the automatic gain control is achieved by means of the linear VGA 120, situated between the first core TIA 110 and the output stage 130. In that regard, gain control (or gain variation) is performed exclusively at the second stage of the TIA 100, which is at the linear VGA 120. With respect to this design, the disadvantage is that the core TIA 110 starts to degrade linearity for large input signals. The higher the gain of the core TIA 110, the better the sensitivity; however, the linearity will be degraded more for such large input signals.
FIG. 2 illustrates another prior art TIA 200, having a core TIA 210, a fixed gain stage amplifier 220 and an output stage 230. In this configuration, gain control is typically performed with external components coupled to the core TIA 210, such as the core TIA feedback resistance Rf. The output is then fed into the fixed gain stage 220 (which substitutes the VGA 120 illustrated in FIG. 1). However, similar to the TIA design of FIG. 1, this approach also suffers from significant disadvantages and drawbacks. In particular, the dynamic range of control is limited, and the frequency response changes with the variation of Rf (Gain). Moreover, in the approach of FIG. 2, circuitry for the input monitor must be located at the input of the TIA 200, which also affects input sensitivity.
In view of the aforementioned disadvantages and drawbacks in the prior art, there is a need for a high sensitivity, high linearity and large dynamic range high speed TIA.